Beam current integrator



w. R. BAKER BEAM CURRENT INTEGRATOR Oct. 25, 1955 2,721,699

2 Sheets-Sheet 1 Filed Aug. 23, 1948 EEEEIZJ BEAM CUR/PEN?" //v TEG/PA 70/? HEA TER SUPPL Y F/LA MEN 7" 5UPPL Y ARC SUPPL Y ACCELERA 77NG VOLTAGE SUPPL V 8 T I m i I L9 QQ$UZ9.Q$)J- I I 7 ma I /0[ /7 '1-- l H i l I 2 I I W]: i I /a /4 l 2 7 I l gl L l INVENTOR. WILL/AM 1P. BAKE/P BY A TTORNEY Oct. 25, 1955 W. R. BAKER BEAM CURRENT INTEGRATOR 2 Sheets-Sheet 2 Filed Aug. 23, 1948 INVENTOR. W/LL/AM R BA KER BY Maw A Tram/Ev United States Patent O BEAM CURRENT KNTEGRATOR William R. Baker, Berkeley, Calif., assignor to the United States of America as represented by the United tates Atomic Energy Commission Application August 23, 1948, Serial No. 45,6ti'7 Claims. (Cl. 235-92) This invention relates to calutrons and more particularly to a beam current integrator for a calutron.

Calutrons are described in general in Atomic Energy for Military Purposes, by H. D. Smyth, and in greater detail in the copending application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9, 1944, now Patent No. 2,709,222, issued May 24, 1955.

Calutrons are principally employed in separating the isotopes of the elements. They are adaptable to the separation of macroscopic amounts of any mixture of isotopes which may be ionized.

In general, an ion generator projects a beam of ions of a polyisotopic material into a magnetic field. Thereafter, the ions travel in curved paths through the magnetic field; the ions of greater mass describing paths with flatter curves than the ions of lighter mass. Collectors are disposed at suitable points along each path, preferably at the 180 point in the curved path, in order to discharge and collect the ions of the different paths. In this manner the atoms of different mass that were originally in the polyisotopic mixtpre are distributed in different regions and thereby substantially separated from one another.

Beam integrators are not new; in fact, ever since cyclotrons were developed to the point where there was enough beam current to detect, some sort of device was necesesary to measure the quantity of beam current versus time. Such measuring circuits dealt with currents in the order of microamperes and, when the calutron was developed with its beam current in the milliampere region, it was neceessary to provide a circuit arrangement that would function in this higher current range.

A simple integrator for this purpose which was fabricated and successfully used consisted of a low leakage condenser shunted by a neon glowlamp, the combination being placed in series with the current path to the collector elements. Beam current flowed into the condenser which became charged to the striking-voltage of the neon lamp and, upon firing discharged the condenser after the fashion of the conventional relaxation oscillator. A mechanical register for counting the number of discharges completed the device; the number of counts being the integral of the beam current over a given period of time. However, for stable operation of such a calutron the necessity of maintaining the potential of the collector electrodes at an even level became manifest; in the preferred type of calutron this potential is at or near ground potential. The simple integrating device referred to does not fulfill this requirement to any satisfactory degree.

The present invention overcomes the difficulties of the earlier integrating circuits by utilizing the gain of a vacuurn tube to keep the collector voltage variations much smaller in magnitude than would be the case in an integrator using only a condenser, a glow tube, and a register.

It is therefore an object of this invention to provide 2,721,699 Patented Oct. 25, 1955 fl fi an improved apparatus for integrating the beam current in a calutron.

Another object of this invention is to provide, in a beam current integrator, an essentially constant collector element potential.

Still another object of this invention is to provide an apparatus for determining the amount of beam current with respect to time.

A still further object of this invention is to provide an apparatus for maintaining the potential of the collecting electrodes constant while obtaining an integral of the beam current with respect to time.

Other objects and advantages of this invention will be apparent to those skilled in the art to which it pertains, upon consideration of the following specifications and drawings in which:

Figure 1 shows a plan view in diagrammatic form of the essential elements of a calutron including the beam current integrator in block form;

Fig. 2 is a schematic diagram of the fundamental circuit of the integrator for illustrative purposes; and

Fig. 3 is a schematic diagram of a complete integrator embodying the principle of the invention.

Referring now more particularly to Fig. 1, it will be seen that ions, produced by an ion source 1, are drawn through an ion exit slit 2 by the accelerating force of the potential applied to the ion accelerating electrodes 3. The ions so accelerated are formed into a beam in passing through a collimating slit 4 between the accelerating electrodes 3, and are acted upon by a magnetic field extending vertically from the plane of the drawing and defined by the pole face 6. The path of the ions is curved by the magnetite field toward a collector element 7 which is connected through the beam current integrator 8 to ground.

For the purpose of illustrating the operation, a simplified circuit of the integrator is shown in Fig. 2. It will be seen that the beam current to be integrated fiows in at terminal 9, through the series circuit comprising a battery 10, a condenser 11, and a triode 12. Triode 12 has its anode connected to the condenser 11 and its cathode connected to ground 13 through a conductor 14. Connected in shunt with the condenser 11 is the series circuit comprising the primary of a transformer 16 and a gaseous discharge device 17. The secondary of the transformer 16 is directly connected to an electromechanical register 18. The grid of triode 12 is connected through a bias battery 19 to the input terminal 9.

The operation of this simplified circuit will now be considered. The beam current flowing in at terminal 9 is stored as a charge on condenser 11. When the voltage on the condenser 11 reaches the firing potential of the gaseous discharge tube 17, the gaseous discharge tube conducts and thereby discharges the condenser 11. The discharge path includes the primary of transformer 16; and the discharge of the condenser 11 produces a pulse in the secondary of transformer 16. This pulse is of sufiicient amplitude to operate the electromechanical register 18.

It is evident that the entire beam current flows through the plate impedance of the triode 12; or more correctly, as positive charge fiows into one side of condenser 11 electrons flow from the cathode to the anode of triode 12 and these electrons flow into the other side of condenser 11 to balance the positive current flowing in. The cathode of the triode 12 is returned directly to ground through wire 14. The effective impedance of the calutron is therefore connected between the input terminal 9 and ground of the integrator. This impedance is quite high, as apparatus of this type tends to act as a constant current generator.

During operation the grid must attain a potential in the operating range of the tube such that the net cathodegrid voltage will allow a plate current to flow which is just equal to the beam current of the calutron. Thus the grid potential is inversely proportional to the gain of the tube. In this manner the potential of the collector element 7 (Figure 1) which is connected to the grid of triode 12 is maintained at a potential near that of ground and which changes by a factor of 1/ amplification factor of the change in beam current.

A rather unorthodox arrangement of components is used in this simplified integrator, that is, the minus side of the plate supply battery 10 is returned directly to the beam collector terminal 9. Thus the plate current of triode 12 is at all times equal to the beam current. If no beam current flows there is likewise an absolute cut off in the plate current of triode 12 and positively no count could be recorded by the register 18. Now, if one milliampere of beam current flows through the circuit the same current appears everywhere in the circuit, the only variable quantity being the bias voltage that appears on the grid of triode 12; exactly enough grid bias appears to allow one milliampere of plate current to flow at Whatever the effective plate voltage is. This could be referred to as a unity-current voltage amplifier, which is about as near as it can be described in orthodox terminology.

The range of this combination would be, at one end, absolute zero beam current and, at the other extreme, whatever current that would bring the grid of the triode to the zero bias level. Naturally, at an excessive current level, the grid would be forced positive in order to allow that much current to flow and the resulting grid current to ground would be lost current that would not flow through the condenser 11 and be recorded. As long as the triode control grid operates in a minus region the tube constants other than the amplification factor have no importance at all. Any source of nonlinearity is then confined to the glow lamp-condenser combination not always firing at the same voltage or to poor collector insulation. This latter problem becomes less and less as the circuit input is made to run close to ground potential.

The purpose of the bias battery is to make the collector operate at near zero voltage with respect to ground and at the same time bias the tube to cut oil? in case the collector becomes short-circuited to ground.

Fig. 3 shows the basic circuit applied to a pentode amplifier tube in which the gain factor is much larger, and hence the stability of the collector potential is much greater. For practical purposes the battery supplies shown in Fig. 2 have been replaced with alternating cur- I rent supplies which are of conventional full wave design.

The screen grid voltage supply 29 shown in Fig. 3 comprises transformer 21, rectifier tube 22, and a pi section filter including the condensers 23 and 24- and the choke 26. A gaseous regulator tube 27 and its series voltage dropping resistor 28 are included to insure a stable output voltage from the power supply.

A second alternating current power supply 29, as plate voltage supply, replaces the battery 10 shown in Fig. 2. This power supply comprises a transformer 31, a rectifier tube 32 and a pi section filter including the condensers 33 and 34 and a choke 36. A bleeder resistor 37 is connected across the output condenser 34 in order to discharge the condensers 33 and 34 when the supply is de-energized.

As in the simplified circuit, the cathode of the vacuum tube 38 is connected to ground 39 through a conductor 41. The anode of the pentode 38 is connected to the input terminal 42 through a condenser 43 and the bleeder resistor 37 of the plate power supply 29. Connected in shunt with the condenser 43 is a series circuit comprising a gaseous discharge tube 44 and the primary of a transformer 46. The secondary of the transformer 46 is connected to an electromechanical register 47 by means of conductors 48 and 49. The control grid of the pentode 38 is connected through a battery 51 to the input terminal 42. The screen grid of pentode 33 is connected to the positive terminal of the screen grid supply 20 through conductor 52, and the suppressor grid and the cathode of pentode 38 are connected together by conductor 53.

In this improved circuit as in the simplified circuit the collector element of the calutron is connected to the input terminal 42 of the beam integrator. The beam current then flows through the plate supply bleeder resistor 37 and into the condenser 43. The pentode 38 passes a charging current which is equal and opposite to the beam current. The effect of these two events is to charge condenser 43 to the firing potential of the gaseous discharge device 44, whereupon the gaseous discharge device 44 fires and discharges the condenser 43. This discharge current passing through the primary of the transformer 46 causes a voltage pulse to appear across the secondary of transformer 46; and such pulse of voltage causes the electromechanical register 47 to operate, adding one more count on the dial. Thus the summation of counts over a given interval of time is the integral of the beam current.

The same unorthodox arrangement of components is used in the pentode circuit as was used in the simplified circuit; that is, the negative side of the plate power supply 29 is returned to the beam collector terminal. Thus the pentode plate current is at all times exactly equal to the beam current. If no beam current flows there is likewise an absolute cutoff in the tube plate current and positively no count could be recorded by the register. Now, if one milliampere of beam current flows through the circuit the same current appears everywhere in the circuit, the only variable quantity being the bias voltage that appears on the control grid of the pentode; exactly enough bias appears to allow one milliampere of plate current to fiow at whatever the effective plate voltage is. The term unity-current voltage amplifier could appropriately be applied to the foregoing arrangement.

The range of this combination would be between the extremes of 1) absolute zero beam current and (2) whatever current that would bring the control grid of the pentode to the zero bias level. Naturally, at an excessive current level, the control grid would be forced positive in order to allow that much current to flow and the resulting control grid current to ground would be lost current that would not flow through the condenser and be recorded. As long as the pentode control grid operates in a negative region the tube constants other than the amplification factor have no importance at all. Any source of nonlinearity is then confined to the glow lamp-condenser combination not always firing at the same voltage or to poor collector insulation. This latter problem becomes less and less as the circuit input is made to run close to ground potential.

The purpose of the bias battery is to make the collector run at near Zero voltage with respect to ground and at the same time bias the tube to cut-off in case the collector becomes short-circuited to ground.

By making this bias variable, it is possible to make the collector run at any voltage with respect to ground that is desired. This follows from the feature brought out previously that the bias on the grid automatically sets itself at the value necessary to allow the beam current to flow; therefore, if a voltage equal to the required bias is inserted in between the collector terminal and the grid of the vacuum tube used, then the actual collector voltage must be substantially zero.

Although I have described my invention with respect to a particular embodiment thereof, it is not limited to this embodiment nor otherwise except by the terms of the following claims.

What is claimed is:

1. In an integrating network having a pair of input terminals, the combination comprising a vacuum tube having at least an anode, a control grid, and a cathode, a condenser having one side connected to said anode and the other side connected to one of said terminals through an anode voltage supply means, said cathode being connected to the other terminal and a ground connection, bias means connected between said control grid and said ungrounded terminal, a gas diode tube circuit connected in parallel with said condenser, and indicating means coupled to said gas diode circuit for counting the number of discharges of said condenser as a function of current at said input terminals.

2. In an integrating network having a pair of input terminals, the combination comprising a vacuum tube having at least an anode, a control grid, and a cathode, a condenser having one side connected to said anode and the other side connected to one of said terminals through an anode voltage supply means, said cathode being connected to the other terminal and a ground connection, bias means connected between said control grid and said ungrounded terminal, a gas diode tube circuit connected in parallel with said condenser, and a mechanical register coupled to said gas diode circuit for indicating the number of discharges of said condenser as a function of current at said input terminals.

3. In an integrating network having a pair of input terminals, the combination comprising a vacuum tube having at least an anode, a control grid, and a cathode, a condenser having one side connected to said anode and the other side connected to one of said terminals through an anode voltage supply means, said cathode being connected to the other terminal and a ground connection, bias means connected between said control grid and said ungrounded terminal, a series circuit including a gas diode tube and a primary winding of a transformer connected in parallel with said condenser, and a mechanical register connected to a secondary winding of said transformer for indicating the number of discharges of said condenser as a function of current at said input terminals.

4. In an integrating network having a pair of input terminals, the combination comprising a vacuum tube having at least an anode, a control grid, and a cathode, a condenser having one side connected to said anode and the other side connected to one of said terminals through a register, a rectifier power supply connected across said resistor with its negative side common to the junction of said resistor and terminal, said cathode being connected to the other terminal and a ground connection, said control grid being connected to the ungrounded terminal, means connected to said control grid for impressing a negative bias thereon with respect to said ungrounded terminal, a series circuit including a. gas diode tube and a primary Winding of a transformer connected in parallel with said condenser, and a mechanical register connected to a secondary winding of said transformer for indicating the number of discharges of said condenser as a function of current at said input terminals.

5. In an integrating network having a pair of input terminals, the combination comprising a vacuum tube having an anode, a suppressor grid, a screen grid, a control grid, and a cathode, said suppressor grid being connected to said cathode, a condenser having one side connected to said anode and the other side connected to one of said terminals through a resistor, a rectifier power supply connected across said resistor with its negative side common to the junction of said resistor and terminal, said cathode being connected to the other terminal and a ground connection, said control grid being connected to the ungrounded terminal, means connected to said control grid for impressing a negative bias thereon with respect to said ungrounded terminal, means connected between said screen grid and cathode for impressing a positive operating voltage thereon, a series circuit including a gas diode tube and a primary winding of a transformer connected in parallel with said condenser, and a mechanical register connected to a secondary winding of said transformer for indicating the number of discharges of said condenser as a function of current at said input terminals.

References Cited in the file of this patent UNITED STATES PATENTS 

